Why does Enceladus have geysers and Mimas–closer to Saturn and an orbit more likely to produce slushiness–not? Maybe Mimas has dried out, so to speak. If the water below has long ago gushed into space what might be left are semi-collapsed caverns and interior rubble. Mimas has a significantly lower density than Enceladus. That might mean that the moon had much less stone originally. Or that the interior water was long lost, and now the interior rubble just floats around a bit instead of layers rubbing to create friction and heating. Low density in small bodies like asteroids is usually attributed to empty spaces within.

Among Saturn’s larger moons (Mimas, Enceladus, Tethys, Dione, and Rhea), Enceladus has the highest density among them. A greater ratio of stone to ice is what scientists think. But as for that lake, 4.5 billion years is a long time to be holding on to a body of water on a moon that small. Definitely worth taking a closer look … someday.

about Todd Flowerday

A Roman Catholic lay person, married (since 1996), with one adopted child (since 2001). I serve in worship and spiritual life in a midwestern university parish.

about John Donaghy

John is a lay missionary since 2007 with a parish in western Honduras. Before that he served in campus ministry and social justice ministry in Iowa. His ministry blog is http://hermanojuancito.blogspot.com

He also blogs reflections on the lectionary and saints/heroes/events of the date at http://walktheway.wordpress.com

He'll be a long-term contributor here analyzing the Latin American bishops' document from their 2007 Aparecida Conference.